Add method for Element.

[fntz]

I added method that returns the text content of element.

For example:

  <div id="element">Lorem<span>ipsum</span> dolore</div> 

  $('element').content(); // returns text for element and nested elements
  //=> Lorem ipsum dolore
  $('element').content(true); // returns text only for element without nested elements. 
  //=> Lorem dolore